The physicians treating growth hormone deficient (GHD) patients with human growth hormone have frequently reported that patients experience an increased quality of life in comparison with a control group not subjected to the treatment. Statistically significant differences were found between the groups regarding social isolation, physical mobility, sleep and emotional status (see Acta Paed Scand (Suppl), v356, p55-59, 1989, S Bjork et al. and Acta Paed Scand (Suppl), v356, p70-72, 1989, G A McCauley) In clinical treatment with human growth hormone some secondary effects on the central nervous system (CNS) have been observed. It has been suggested that opioid active peptide fragments released from growth hormone may reach the CNS if the human plasma contains proteolytic activity for releasing them. If such fragments can pass through the blood-brain barrier, they may affect the CNS. These previous studies indicate that human growth hormone affects the CNS and suggests that enzymatically released fragments may interfere with opioid receptors.
A number of studies have shown that enzymatically treated preparations of proteins can include peptides with opioid activity such as .beta.-casomorphin, cytochrophins and hemomorphins. .beta.-casomorphin originates from degraded beta-casein peptone and is previously disclosed in Physiol Chem, v360, p 1211-16, 1979, V Brandl et al.; Pharmacol Sci, v4, p193, 1979, V Brantl et al.; Eur J Pharmacol, v106, p213-214, 1984, V Brantl et al. and J Clin Endocrinol Metab, v68, p283-9, 1989, F Nyberg et al.
It has also been shown that enzymatically derived fragments of mitochondrial cytochrome b contain cytochrophins, another opioid peptide (see Eur J Pharmacol, v111, p293, 1985, V Brantl et al). For a reference of hemomorphins see Eur J Pharmacol, 125, p 309-10,1986, V Brantl et al. The opioid activity of these peptides were confirmed by testing their inhibition of the electrically induced contractions of the guinea-pig ileum myentric plexus longitudinal muscle preparation (GPI-assay) as well as by receptor assay.
Certain cyclic oligopeptides with opioid receptor activity have previously been disclosed by J De Maio et al. in Proc. Natl. Acad. Sci., Vol. 77(12), 1980, p 7162-6. This article discloses a number of prepared cyclic enkephalin analogs. Cyclic oligopeptides with opioid receptor affinity are also disclosed in J Med Chem, Vol. 35, 1992, p 3956-3961, P Schiller et al. U.S. Pat. No. 4,254,024 (J. Stewart et al.) discloses a class of tetrapeptides demonstrated to have opiate activity with a guinea pig ileum strip test having the general formula H-Tyr-X-Y-Z. Another reference that discloses opioid receptor binding straight tetrapeptides is European patent application EP 350 221.
In a previous study, two different peptidases were investigated for their ability to release fragments of human growth hormone, which may interfere with opioid receptors. The enzymes were a commercially available trypsin and an endopeptidase partially purified from human plasma. The fragments were separated on reversed phase HPLC and subsequently analyzed by an opioid receptor assay performed with synaptic plasma membranes from rat brains (without cerebellum). The results indicated that receptor active fragments were released both by trypsin and the endopeptidase. However, in a guinea-pig ileum myenteric plexus/longitudinal muscle preparation (GPI) assay, these fragments were found to be less potent than beta-casomorphins (fragments of casein peptone). These findings were published at the IV Meeting of the European Neuroendocrine Association (Santiago de Compostela 28-30 Jun. 1989).